Developments in internal combustion engines for motor vehicles focus on reducing exhaust emissions and fuel consumption. One approach for reducing fuel consumption and emissions is to adapt the operation of the various ancillary units, which for example include the coolant pump or lubricating oil pump, more precisely to the requirements of the engine. In the case of coolant pumps, which are a preferred use of the rotary pump, these efforts are aimed at more rapidly heating the engine following a cold start and at reducing the operational rate needed for the coolant pump, in particular at a high rotational speed of the engine. Mass-produced designs such as electrically driven coolant pumps and switchable friction roller drives make considering other alternatives seem worthwhile with regard to cost and reliability. The split ring slider represents an approach, which has been known for decades, for influencing the delivery characteristics of turbines as well as compressors and pumps having a radial design, wherein an annular slider which encompasses the feed wheel of the pump on the outer circumference is axially shifted, forming an annular gap, and the flow cross-section on the outer circumference of the feed wheel is thus varied. The annular slider acts as a shutter in the outflow region of the feed wheel.
The volume of fluid delivered by rotary pumps per unit time, referred to in the following as the delivery volume, changes with the rotational speed of the pump. In displacement-type rotary pumps, the delivery volume is proportional to the rotational speed of the pump, since such pumps exhibit a constant specific delivery volume, at least in the rotational speed range which is relevant for practical purposes. “Specific delivery volume” refers to the volume of fluid delivered per revolution. Fluid-flow machines such as for example centrifugal pumps do not have this proportionality; the delivery volume even increases disproportionally with respect to the rotational speed. If the rotary pump is rotary-driven by a combustion engine in a fixed rotational speed relationship to an output shaft of the combustion engine, for example a crankshaft, as is the case in preferred uses, the proportionality or in principle the dependency between the delivery volume and the rotational speed can be disruptive in particular rotational speed ranges of the combustion engine. Thus, for example, beyond a rotational speed of the engine of about 2000 rpm, lubricating oil pumps for supplying drive motors of motor vehicles deliver more lubricating oil than is required for lubricating the combustion engine. Coolant pumps, which in most applications are embodied as centrifugal pumps, show similar characteristics. If the respective pump delivers more fluid than is actually needed, energy for driving the pump is wasted. Undesirable side-effects can also occur. In the case of lubricating oil pumps, for example, delivering too much lubricating oil can cause the crankshaft to flounder in the lubricating oil, thus creating further losses. The delivered fluid which is surplus to requirement can for example be conveyed back into the fluid reservoir via a bypass, although this needlessly consumes drive energy for the pump.
In order to better adapt the delivery volume of rotary pumps to requirements, rotary pumps which can be adjusted, for example merely controlled or also regulated, in terms of delivery volume have been developed. Thus, for example, EP 1 363 025 B1, which is incorporated by reference, describes toothed wheel pumps which can be regulated. A vane cell pump which can be regulated is for example known from DE 10 2010 009 839 A1, which is incorporated by reference.
EP 2 489 881 A2, which is incorporated by reference, discloses a centrifugal pump which has a radial design and can be regulated, and its use as a coolant pump. The centrifugal pump comprises a radial feed wheel for delivering the working fluid, which can in particular serve as a coolant for a combustion engine, and also a servo pump for fluidically adjusting a setting structure which, when adjusted, alters the delivery volume of the centrifugal pump. The servo pump is embodied as a rotary pump and co-operates with a control valve via which the fluid delivered by the servo pump is applied to the setting structure. Above a lower rotational speed range, the delivery volume of the servo pump is high enough that the volume flow cannot flow quickly enough through the control valve when the valve is open, and a back-pressure can therefore be created which acts undesirably on the setting structure. In order to prevent this, a pressure limiter via which fluid can flow back into the cycle is provided downstream of the outlet of the servo pump. This corresponds to the bypass solution mentioned at the beginning.